QU et al.: REAL-TIME ROBOT PATH PLANNING BASED ON A MODIFIED PULSE-COUPLED NEURAL NETWORK MODEL 1725
It is rigorously proved that the generated trajectory does not
suffer from undesired local minima and is globally optimal in a
stationary environment. However, these models require that the
robot dynamic is faster than the target and obstacle dynamics,
and have difficulty in dealing with fast changing environments
[34]. Inspired by the dynamic properties of Hodgkin and
Huxley’s membrane model [35] for a biological neural system
and the later developed Grossberg’s shunting model [36], [37],
Yang and Meng [38] proposed a new neural network approach
for dynamic environments. This neurodynamics approach is
later extended to various robot systems [39]–[45], and further
inspires the development of a distance-propagating system for
robot path planning [22], [23]. Low
et al. [47] presented a co-
operative extended Kohonen maps (EKMs) to achieve complex
robot motion, and later they [48] described a distributed layered
architecture for resource-constrained multirobot cooperation.
Those two methods are able to avoid local minima such as
concave obstacles as well as dynamic environments.
A pulse-coupled neural network (PCNN) is a biologically
plausible computational algorithm, which is similar to the
locally excitatory globally inhibitory oscillator network (LE-
GION) model proposed by Wang et al. for real-time image
segmentation, figure/ground segregation, and many other ap-
plications [49], [50]. PCNNs are capable of emulating the
behavior of cortical neurons as observed in the visual cortices
of cats [51]. Since Johnson’s work [52]–[54], there has been
increased interest in using PCNNs for various applications,
such as target recognition [55], image processing [56], motion
matching [57], pattern recognition [58], and optimization [59].
Some recent research shows that the spatio–temporal dynamics
of PCNNs provide good computational capability for solving
some optimization problems. In 1999, Caulfield and Kinser
[59] presented the idea of utilizing the autowave in PCNNs
to find the solution to the maze problem. Their model can
find the shortest path quickly and with minimum effort, where
the solution is related to the length of the shortest path and
independent to the path graph complexity. However, many
neurons are needed to find the shortest path in large mazes or
graphs, since one pulse of the coupled neuron corresponds to
a unit length of path [60].
In this paper, a novel real-time collision-free robot-path-plan-
ning approach is proposed based on a modified pulse-coupled
neural network (MPCNN). The proposed model is topologically
organized with only local lateral connections among neurons.
It needs fewer neurons than Caulfield and Kinser’s approach
[59], since the pulse propagation does not correspond to a unit
length of path. Instead, the generated spiking wave in the pro-
posed network spreads at a constant speed so that the time of
travel between two neurons is proportional to the path length
between them. Whenever the sensory systems (either onboard
or installed in the workspace) detect a change in the dynamic
environment, a new path is calculated in the same way. The
computational complexity of the algorithm is only related to the
length of the shortest path, and independent of the workspace
complexity and the number of existing paths in the map. Each
neuron in the proposed model propagates a firing event to its
neighboring neuron without any comparison computations. The
proposed model also works in real time and requires no prior
knowledge of target or barrier movement, no explicit optimiza-
tion of any cost functions, and no explicit searching over the free
workspace or collision paths. It is, therefore, useful for real-time
robot path planning in dynamic environments, without the need
of any learning procedures.
Similar to many existing path-planning methods [21], [22],
[38], in the proposed approach to real-time robot path planning,
the complete knowledge of the current environment is required.
In particular, it is assumed that the locations of the robot, obsta-
cles, and targets are completely and accurately known through
varioussensor measurements,multisensor fusion,and signalpro-
cessing systems. The autonomous navigation of mobile robots is
verycomplicatedandinvolvesmanyissues,suchasreal-timepath
planning, multisensor fusion, signal processing, and motion con-
trol. The sensor placement and multisensor fusion needed to ob-
tain complete environment knowledge, the signal processing re-
quired to remove sensor measurement and communication noise
for accurate environmental information, and the motion control
systems needed to drive the robot wheels are beyond the scope
of this paper. In indoor and closed environments, the complete
knowledge of the workspace can be obtained through several
charge-coupled device (CCD) cameras mounted over the ceiling
and various onboard robot sensors. In outdoor and open envi-
ronments, knowing the environment is a challenging task, which
could possibly be achieved through global positioning system
(GPS), land marks, laser sensors, ultrasonic sensors, and var-
ious other sensors [61]. Related work on real-time path plan-
ning of mobile robots with limited onboard sensory informa-
tion in completely or partially unknown environments is found
in [41], [42], and [62]. Knowing the accurate locations of the
obstacles and robot in the environment at every instant can be
addressed with simultaneous map building/updating and local-
ization methods [41], [63], [64]. Some approaches for real-time
navigation of mobile robots have no explicit global path-plan-
ning algorithms. These employ human-like or biologically in-
spiredstrategies,suchasneurofuzzyandbehavior-basedmethods
[61], [65], where the robot movement is determined by the real-
time sensor measurements and only simple local path planning
is available.
The remainder of this paper is organized as follows. The
proposed modified PCNN is described and studied theoretically
in Section II. Algorithms for robot path planning, based on
the MPCNN, are presented in Section III. Simulation results
are given in Section IV. Section V discusses parameter setting
for the proposed model. Finally, conclusions are drawn in
Section VI.
II. MPCNN M
ODEL FOR ROBOT PAT H
PLANNING
In this section, an MPCNN model is proposed for real-time
robot path planning. A simple description of the original PCNN
is described in the Appendix. The performance of the proposed
model is analyzed mathematically. In addition, many variables
are defined and used in this section. The main symbols and def-
initions used in this paper are summarized in Table I.
A. Network Architecture
The neural network architecture of the proposed model is a
discrete topologically organized map and can be expressed in a